This invention generally relates to ultrasound color flow Doppler imaging of fluid flow fields. In particular, the invention relates to a method and an apparatus for improving the display of such imaging.
Ultrasonic scanners for detecting blood flow based on the Doppler effect are well known. Such systems operate by actuating an ultrasonic transducer array to transmit ultrasonic waves into the object and receiving ultrasonic echoes backscattered from the object. In the measurement of blood flow characteristics, returning ultrasonic waves are compared to a frequency reference to determine the frequency shift imparted to the returning waves by flowing scatterers such as blood cells. This frequency, i.e., phase shift, translates into the velocity of the blood flow. The blood velocity is calculated by measuring the phase shift from firing to firing at a specific range gate.
The change or shift in backscattered frequency increases when blood flows toward the transducer and decreases when blood flows away from the transducer. Color flow images are produced by superimposing a color image of the velocity of moving material, such as blood, over a black and white anatomical B-mode image. Typically, color flow mode displays hundreds of adjacent sample volumes simultaneously, all laid over a B-mode image and color-coded to represent each sample volume's velocity.
Typically, color flow processors estimate blood flow velocity, blood flow power, and blood flow variance. Typically, color flow data is used to modify the color of a region of interest on a display screen. The user selects the type of data used for the display. The modes typically available are power only, velocity only or velocity and variance combined.
In current ultrasound scanners, various color flow display parameters are either fixed with no user selectability or are preset to some specific setting and can only be changed if action is taken by the user, one parameter at a time. This limits image quality and user productivity for any given application and scanning situation. There is a need for a scanner in which these same parameters can all be automatically adjusted at the same time to optimize image quality related to color flow display for a specific scanning situation, thus increasing user productivity.
In the color flow power or color flow velocity modes of operation, known ultrasound scanners provide a B/color priority threshold which is user selectable from a softkey menu on the user's console of the scanner. The threshold may be set by the user to various percentages of the maximum B-mode gray scale value. For any pixel within the color mode region of interest (ROI), if the B-mode pixel value exceeds the selected B/color priority threshold, then the B-mode value is displayed for that pixel. Otherwise, the corresponding color pixel value is displayed, if there is one. However, the actual B-mode data maximum value may vary over a wide range. As a result, the threshold is frequently less than optimal. Accordingly, there is a need for a color flow ultrasound scanner which can automatically adjust the B/color priority threshold according to the actual B-mode data.